1. Field of the Invention
The present invention relates to an optical telecommunication system that is provided with an automatic channel switching mechanism between two symmetrical fiber channels, such that optical signals can be transmitted and received over the communication line transparently with high efficiency and reliability.
2. The Related Art
To increase the data reliability in optical telecommunication, the most common practice is to use multiple fiber channels simultaneously connecting between the transmitting and receiving ends of the communication line. If the telecommunication through one of the fiber channels is disconnected, the system notifies the service personnel who will then try to repair the damaged channel and manually switch the signal transmission path to another open channel.
The data communication may be disrupted, and the response time and manual switching process may hold up the signal transmission for considerable length of time before the communication line can resume its normal service. Consequently someone proposed a technique of automatic channel switching. There are different ways of channel switching, one of which employs a main controller and multiple fiber channels, including a primary channel and a spare channel. If the primary channel is disconnected, the system uses the interconnected signal lines to notify the optical switches on both ends of the communication line to switch to the spare channel simultaneously. However, the cost for establishing extra signal lines is quite heavy, thus many telecommunication system builders are discouraged.
A prior art design disclosed a more economical method, which used an automatic channel switching among multiple fiber channels. When data are transmitted over a fiber channel, the specific fiber channel is systematically locked by the optical switches on two ends, and when no more data are present the optical switches are then be released. The dynamic channel selection process will start again to find another active channel for lock-in. Since the optical switches on both ends are operated independently, this design can avoid the complicated intercommunication on both ends. However, one potential problem is that the optical switches may engage in a ‘racing’ condition in an attempt to out run each other, thus failing to lock in any one channel. To correct this situation, there shall be a controller to arbitrate over the channel selection.
Another prior design proposed to send put data signals simultaneously on two symmetrical channels at the same time, and the power meters were installed on the receiving end to monitor the power level of transmitted signals. When the power meter detects that one of the two channels has higher power level, the channel will be selected as the working channel and the other channel as the spare channel. This can avoid the complicated intercommunication between the optical switches on two ends and the ‘racing’ problem. But one of the more serious problems in this case is that the optical switches on two ends may be using different channels to transmit data signals at the same time, so it could be that data were sent out over one channel on one end, while the same channel was being shut down for maintenance.
Moreover, there is another problem commonly shared by all the above schemes from the fact that the spare channel has not been actively monitored. If a line disconnection had occurred over the primary channel, the system that was trying to switch to the spare channel would only find it disconnected.
In these aspects, the optical telecommunication system with automatic channel switching according to the present invention can substantially reduce or obviate the limitations and disadvantages of the prior art.